$\text{Câu 5:}$
`E=(1/99+2/98+3/97+...+99/1)/(1/2+1/3+1/4+...+1/100)`
`=((1/99+1)+(2/98+1)+(3/97+1)+...+(98/2+1)+1)/(1/2+1/3+1/4+...+1/100)`
`=(100/99+100/98+100/97+...+100/2+100/100)/(1/2+1/3+1/4+...+1/100)`
`=(100.(1/99+1/98+1/97+...+1/2+1/100))/(1/2+1/3+1/4+...+1/100)`
`=100`
`F=(94-1/7-2/8-3/9-...-94/100)/(1/35+1/40+1/45+...+1/500)`
`=5.((-1/7+1)+(-2/8+1)+(-3/7+1)+...+(-94/100+1))/(5.(1/35+1/40+1/45+...+1/500)`
`=5.(6/7+6/8+6/9+...+6/100)/(1/7+1/8+1/9+...+1/100)`
`=5.6.(1/7+1/8+1/9+...+1/100)/(1/7+1/8+1/9+...+1/100)`
`=30`
`⇒ 2.F=2.30=60`
`⇒ E-2.F=100-60=40`
